1. Field of the Invention
The present invention relates to a manufacturing method of a semiconductor memory device, and more particularly to a simplified wafer quality testing and repairing process of a semiconductor memory device achieving higher productivity of memory devices such as DRAMs, SRAMs, etc., which have a redundancy circuit.
2. Description of the Related Art
The current increasing integration trend of memory devices allows shortening of the distance between lines, so defects tend to increase throughout the manufacturing process, which seriously reduces yields. Therefore, semiconductor manufacturers have adopted a redundancy technique for achieving higher productivity by restraining the yield decrease which may result from processing deficiencies. The redundancy technique replaces a slightly defective circuit resulting from poor processing with a reserve circuit in repairable chips.
For example, in a semiconductor memory circuit, quality enhancement is achieved by integrating into chips reserve blocks of reserve rows and columns, and replacing the row or column of a block containing a faulty bit of a regular cell array with a reserve row/column block. This redundancy technique is very effective in DRAMs and SRAMs in which cells of identical function are arranged. To replace a faulty row or column of a memory device having a faulty bit with a fully functional row or column, a program device and method for deactivating the faulty row/column and activating the reserve one is required. The best-known redundancy program device and method therefor is a fuse composed of polysilicon resistors, and the like, and an electrical fuse method for electrically blowing the fuse. Another redundancy device and method therefor is a link of polysilicon, polycide, etc., and a laser beam method for cutting off this link by applying the laser beam.
The electrical fuse method requires a transistor for high current driving, control circuits and a special pad for supplying current, etc., for cutting off the fuse, to be integrated onto the chips. The required inclusion of the circuits needed to cut the fuse is disadvantageous because they occupy too much chip area, and significantly delay program access time. However, the electrical fuse method is advantageous because testing and repairing equipment are inexpensive and high reliability is achievable by protecting the fuse portion with a protective film.
The laser beam method is very expensive because the initial cost of the testing and repairing equipment is very high, and high throughput is required to stabilize the laser beam and to determine the exact position of the laser beam. However, the laser beam method is advantageous, for the redundancy circuit design is easy and a plurality of links can be arranged in a very small area in the chip economically utilizing the chip area. Accordingly, due to the current ultra-minimization and high integration trends of semiconductor memory devices, the laser beam method is becoming more prevalent.
The wafer testing process of the laser beam method comprises a pre-laser testing step, a laser repairing step, and a final quality classifying step. To shorten the test time while maintaining the device's characteristics and quality, a method has been adopted by which a circuit with enough flexibility for designing and processing is to be searched and the test item with no defect is to be skipped. However, defective chips can be include in the skipped items which can be caused by process variables shifting frequently thereby inevitably reducing the yield in the subsequent package testing process.
Consequently, a new method is desired to enable the final quality classifying step to be skipped, while increasing the package yield in the wafer testing process of a redundancy memory product.